1895.] lOEITJS FIATOPALLIATUS AND PSITTACTJS ERITHACTTS. 369 



slightly grooved antero-posteriorly, especially in the anterior 

 portion of each. But in P. erithacus these cannot be said to be 

 more than rather flattened. 



The ventral surface of the prosopium, behind the palate, shows, 

 in both species, a median antero-posterior ridge with a wide 

 concavity on either side of it, in the hinder part of which is a 

 deepish fossa, beneath which the palatine passes forwards and 

 external to which is the fossa for the zygoma. The median ridge 

 projects backwards as a process from the postaxial margin of this 

 postpalatal part of the ventral surface of the prosopium, which 

 margin is otherwise slightly concave. The median ridge is less 

 marked in L. favopalliatus and the surface on either side of it is 

 entire, while in P. erithacus it presents a bony network of diploe. 

 This surface is much longer relatively in L. flavopalliatus. 



The ANTERIOR ASPECT of the prosopium (see fig. 8, p. 382) is very 

 similar in both species. Its outline approximates to that of an 

 isosceles triangle with the base dorsad — the basal line being very 

 slightly convex and the two lateral lines being convex towards the 

 base and concave (more strongly so in L. Jlavopalliatus) towards 

 the apex. In addition to the distinctive characters given in the 

 description of the general anterior aspect of the skull, the following 

 points may be mentioned : — Thenares in L. fiavopalUatus are more 

 medianly approximated and nearer the uppermost margin of the 

 prosopium than in P. erithacus, while the lamella of bone between 

 each nostril and the tomial margin is relatively wider. In the 

 latter the lachrymal process is more marked and projects more 

 outwards. In L. Jlavopalliatus it hardly projects at all outwards, 

 but only backwards. The most considerable difference is the greater 

 extension ventrad of the apex of the prosopium (relatiyrely as well 

 as absolutely) in P. erithacus. 



The posterior aspect of the prosopium (which cannot of course 

 be well seen till this part is detached from the cranium) shows, in 

 P. erithacus, an irregular surface which rises, at a moderately obtuse 

 angle, from the hinder margin of the postpalatal ventral surface of 

 the prosopium. The median ridge just described as existing on that 

 surface is continued upwards {mr) in the middle of the posterior 

 surface with a marked concavity on either side of the vertical 

 grooves, which define, laterally, that ascending median ridge. Ex- 

 ternally to this median portion of bone (with its ascending ridge and 

 two lateral concavities) is on either side a large aperture, the two 

 ioTnivag the posterior prosojnal nares{pyi). Each is an oval aper- 

 ture, longer than broad and inclining outwards towards its ventral 

 boundary. These nares and the whole prosopium are bounded 

 dorsally by a transverse bar of bone (grooved posteriorly), the outer 

 end of which projects outwards and slightly upwards, forming the 

 lachrymal process (Ip). The outer boundary of the posterior nasal 

 opening is formed by a vertical bar of bone (one of the two external 

 nasal crura) which descends from the lachrymal process and outer 

 end of the dorsal horizontal bony bar, first narrowing downwards 

 and then expanding beneath its lower end in the pit for the zygoma. 



Peoc. Zool. Soc— 1895, No. XXIV. 24 



